/*
 * ProGuard -- shrinking, optimization, obfuscation, and preverification of Java bytecode.
 *
 * Copyright (c) 2002-2018 GuardSquare NV
 *
 * This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public
 * License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later
 * version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
 * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along with this program; if not, write to the Free
 * Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */
package proguard.classfile.instruction;

import proguard.classfile.*;
import proguard.classfile.attribute.CodeAttribute;
import proguard.classfile.instruction.visitor.InstructionVisitor;

/**
 * This interface describes an instruction that branches to a given offset in the code.
 *
 * @author Eric Lafortune
 */
public class BranchInstruction extends Instruction {
    public int branchOffset;

    /**
     * Creates an uninitialized BranchInstruction.
     */
    public BranchInstruction() {}

    /**
     * Creates a BranchInstruction with the given branch offset. The branch offset is relative to this instruction's
     * offset.
     */
    public BranchInstruction(byte opcode, int branchOffset) {
        this.opcode = opcode;
        this.branchOffset = branchOffset;
    }

    /**
     * Copies the given instruction into this instruction.
     * 
     * @param branchInstruction the instruction to be copied.
     * @return this instruction.
     */
    public BranchInstruction copy(BranchInstruction branchInstruction) {
        this.opcode = branchInstruction.opcode;
        this.branchOffset = branchInstruction.branchOffset;

        return this;
    }

    // Implementations for Instruction.

    public byte canonicalOpcode() {
        // Remove the _w extension, if any.
        switch (opcode) {
            case InstructionConstants.OP_GOTO_W:
                return InstructionConstants.OP_GOTO;

            case InstructionConstants.OP_JSR_W:
                return InstructionConstants.OP_JSR;

            default:
                return opcode;
        }
    }

    public Instruction shrink() {
        // Do we need an ordinary branch or a wide branch?
        if (requiredBranchOffsetSize() == 2) {
            // Can we replace the wide branch by an ordinary branch?
            if (opcode == InstructionConstants.OP_GOTO_W) {
                opcode = InstructionConstants.OP_GOTO;
            } else if (opcode == InstructionConstants.OP_JSR_W) {
                opcode = InstructionConstants.OP_JSR;
            }
        } else {
            // Can we provide a wide branch?
            if (opcode == InstructionConstants.OP_GOTO || opcode == InstructionConstants.OP_GOTO_W) {
                opcode = InstructionConstants.OP_GOTO_W;
            } else if (opcode == InstructionConstants.OP_JSR) {
                opcode = InstructionConstants.OP_JSR_W;
            } else {
                throw new IllegalArgumentException("Branch instruction can't be widened (" + this.toString() + ")");
            }
        }

        return this;
    }

    protected void readInfo(byte[] code, int offset) {
        branchOffset = readSignedValue(code, offset, branchOffsetSize());
    }

    protected void writeInfo(byte[] code, int offset) {
        if (requiredBranchOffsetSize() > branchOffsetSize()) {
            throw new IllegalArgumentException(
                "Instruction has invalid branch offset size (" + this.toString(offset) + ")");
        }

        writeSignedValue(code, offset, branchOffset, branchOffsetSize());
    }

    public int length(int offset) {
        return 1 + branchOffsetSize();
    }

    public void accept(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset,
        InstructionVisitor instructionVisitor) {
        instructionVisitor.visitBranchInstruction(clazz, method, codeAttribute, offset, this);
    }

    public String toString(int offset) {
        return "[" + offset + "] " + toString() + " (target=" + (offset + branchOffset) + ")";
    }

    // Implementations for Object.

    public String toString() {
        return getName() + " " + (branchOffset >= 0 ? "+" : "") + branchOffset;
    }

    // Small utility methods.

    /**
     * Returns the branch offset size for this instruction.
     */
    private int branchOffsetSize() {
        return opcode == InstructionConstants.OP_GOTO_W || opcode == InstructionConstants.OP_JSR_W ? 4 : 2;
    }

    /**
     * Computes the required branch offset size for this instruction's branch offset.
     */
    private int requiredBranchOffsetSize() {
        return (short)branchOffset == branchOffset ? 2 : 4;
    }
}
